What are you defining as a disaster? The drive where the databases fails? The server fails? The building where your servers are hosted from is destroyed?

If your not shipping your backups offsite or to a device which is external from your server every 15 minutes in line with the frequency of your transaction logs, there is the possibility that you could lose everything even though you have done backups, due to the fact that your server is dead, the files live on the server and no where else or the building is destroyed and you cant get into the building to get the server to plug it in at another data centre.